System, method, and apparatus for playing back a plurality of video elementary streams with one playback channel

ABSTRACT

A system, method, and apparatus for playback of multiple video elementary streams is presented herein. A host processor modifies the video elementary streams to allow a transport demultiplexer to distinguish among the plurality of the video elementary streams.

RELATED APPLICATIONS

[0001] [Not Applicable]

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] [Not Applicable]

[0003] [MICROFICHE/COPYRIGHT REFERENCE]

[0004] [Not Applicable]

BACKGROUND OF THE INVENTION

[0005] The MPEG-2 standard represents video sequences by video elementary streams. Video elementary streams represent the raw output of a video encoder that compresses the video sequences and can be associated with other elementary streams, such as an audio elementary stream. The video elementary stream and associated other elementary streams after PES packetisation form what is known as a program. The PES streams so formed from Video and associated other streams are packetized into fixed length transport packets for transmission over a communication medium. The transport packets are transported as a stream (a transport stream) over a communication channel for decoding by a decoder.

[0006] The transport stream can include any number of programs multiplexed together for transport over a communication channel. Each program may use a different compression factor and bit rate that can change dynamically, even though the overall bit rate stays constant. The foregoing is known as statistical multiplexing. A decoder must be able to change from one program to the next and correctly select the appropriate video, audio, and other associated elementary streams.

[0007] The decoder demultiplexes the transport packets using a combination of parameters and tables. The transport packets include a header with packet identification parameter. The packet identification parameters correspond to entries in a program access table and Program Map Table that is present in the transport stream.

[0008] Once the video and audio elementary streams are demultiplexed and extracted from the transport stream, the video and audio elementary streams can be stored separately for future playback. The video and audio elementary streams are usually stored in a high capacity memory, such as a hard disc drive.

[0009] Some trick mode schemes now allow for simultaneous playback of multiple video elementary streams. For example, a feature known as Picture in Picture includes a primary video with another video displayed in a small section of the screen. The foregoing can be achieved in decoders with multiple playback channels. Additional playback channels are needed because after the video elementary streams are extracted from the transport stream, the video elementary streams are not readily distinguishable from one another.

[0010] However, addition of playback channels to decoder systems requires additional hardware and increases costs.

[0011] Further limitations and disadvantages of convention and traditional systems will become apparent to one of skill in the art through comparison of such systems with the invention as set forth in the remainder of the present application with reference to the drawings.

BRIEF SUMMARY OF THE INVENTION

[0012] Aspects of the present invention are directed to a system, method, and apparatus for playing back a plurality of video elementary streams with one playback channel is presented herein. A video decoder decodes and displays a plurality of video elementary streams stored in a hard disc drive. During playback of the plurality of video elementary streams, a host processor modifies the video elementary streams to allow remaining hardware and software to distinguish the various portions of one video elementary stream from another.

[0013] In one embodiment, the host processor breaks the video elementary stream into fixed length packets, wherein the pictures in the video elementary stream are aligned with the start of the fixed length packets. The host processor provides packets containing single pictures from each video elementary stream in a predetermined ordering scheme. The predetermined ordering scheme can include, for example, a round robin scheme. Responsive thereto, a transport demultiplexer places the data from each of the video elementary streams into a corresponding plurality of buffers.

[0014] In another embodiment, the Host processor breaks the video elementary stream into fixed length packets. It only prepends the fixed length packet that starts with a non-slice start code (that indicates the beginning of a picture (or Video Access Unit) with a header information. The header information tells the number of fixed length packets after which another picture (or Video Access Unit) starts. This method ensures that the host processor need not to do too much processing.

[0015] In another embodiment, the host processor breaks the video elementary stream into fixed length packets and prepends each fixed length packet with a header byte containing an identifier identifying the video elementary stream.

[0016] These and other advantages and novel features of the present invention, as well as illustrated embodiments thereof will be more fully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

[0017]FIG. 1 is a block diagram of a transport stream carrying a video stream;

[0018]FIG. 2 is a block diagram of an exemplary decoder system in accordance with an embodiment of the present invention;

[0019]FIG. 3 is a block diagram of an exemplary index table in accordance with an embodiment of the present invention;

[0020]FIG. 4 is a block diagram describing modifications to the video elementary stream in accordance with an embodiment of the present invention;

[0021]FIG. 5 is a flow diagram for displaying a plurality of video elementary stream in accordance with an embodiment of the present invention; and

[0022]FIG. 6 is a block diagram describing modifications to the video elementary stream in accordance with another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0023] Referring now to FIG. 1, there is illustrated a block diagram of a transport stream carrying a video stream. A video sequence 105 comprises a series of frames 110. In a progressive scan, the frames 110 represent instantaneous images, while in an interlaced scan, the frames 110 comprise two fields each of which represent a portion of an image at adjacent times.

[0024] Each frame 110 comprises a two-dimensional grid of pixels 111. The two-dimensional grid of pixels 111 is divided into 8×8 segments 112. The MPEG standard takes advantage of spatial and temporal redundancy to compress the 8×8 segments. Each 8×8 segment is represented by a data structure known as a macroblock 113. The first macroblock in each row includes a row start code 113 a.

[0025] The macroblocks 113 are grouped in what are known as slice groups. Each of the macroblocks 113 belonging to a slice group is stored in a data structure known as a slice 114. A slice 114 is commenced by a slice start code 114 a. Each of the slices 114 associated with the frame are stored together in a data structure known as a picture 115. The picture 115 is a compressed representation of a frame and is also referred to as a video access unit (VAU). The pictures 115 are then grouped together as a group of pictures 120. Groups of pictures 120 are then stored, forming what is known as a video elementary stream 125.

[0026] The video elementary stream 125 is then broken into variable size segments that are packetized, forming packetized elementary stream (PES) packets 130. The PES 135 is then broken into fixed length segments. In MPEG-2, the fixed length is usually 188 bytes. Each fixed length segment forms a payload 140 a portion of a transport packet 140. The transport packet 140 also includes at least four header bytes 140 b with various parameters. The transport packets 140 are transported as a stream (a transport stream) over a communication channel for decoding by a decoder.

[0027] Any number of program streams can be multiplexed together for transport over a transmission over a communication channel. Each program may use a different compression factor and bit rate that can change dynamically even though the overall bit rate stays constant. The foregoing is known as statistical multiplexing. A decoder must be able to change from one program to the next and correctly select the appropriate audio and data channels.

[0028] Referring now to FIG. 2, there is illustrated a block diagram of an exemplary decoder system 200 in accordance with an exemplary embodiment of the present invention. The decoder system 200 comprises a host processor 205, a video decoder 210, a memory controller 215, a video buffer 220, a transport demultiplexer 225, a playback data feeder 230, a hard disc drive 235, and an index table 237.

[0029] The transport demultiplexer 225 receives any number of input channels 240 carrying transport streams 140. The transport streams 140 are processed by the transport demultiplexer 225 to extract elementary streams 125 and stored in the buffer 220. The transport demultiplexer 225 is also used for video playback.

[0030] The buffer 220 comprises a pre-hard disc drive buffer 220 a, a post hard disc drive buffer 220 b, and a video buffer 220 c. The extracted elementary streams 125 are stored in the pre-hard disc drive buffer. The host processor 205 transfers the extracted elementary streams 125 from the pre-hard disc drive and writes the extracted elementary streams 125 to the hard disc drive 235.

[0031] When the extracted elementary stream is written to the pre-hard disc drive buffer 220 a, an entry is logged into the index table 237. The index table stores start codes, such as, for example, pictures start codes, stream header start codes, and GOP header start codes. Each start code stored in the index table 237 is associated with an address indicator storing the address in the pre-hard disc drive 220 a where the start code is stored.

[0032] During playback, the host processor 205 puts the video elementary stream 125 stored in the hard disc drive 235 into the post hard disc drive buffer 220 b. The playback data feeder 230 feeds the data from the post hard disc drive buffer 220 b to the transport demultiplexer 225. The transport demultiplexer 225 places the played back stream into the video buffer 220 c. The data in the video buffer 220 c is decoded and displayed by the video decoder 210.

[0033] The video buffer 220 c can be configured by the host processor 205 to comprise any number of other buffers 220 c(1) . . . 220 c(n), wherein each buffer stores a particular video elementary stream 125 for playback. When a plurality of video elementary streams 125 are played back, the demultiplexer stores each of the video elementary streams 125 played back in a particular one of the buffers 220 c(1) . . . 220 c(n).

[0034] Referring now to FIG. 3, there is illustrated a block diagram of an exemplary index table 237 in accordance with an embodiment of the present invention. The index table 237 comprises any number of records 305. Each record 305 includes a start code 310 and an address identifier 315, wherein the address identifier 315 stores the address in the buffer 220 where the start code is stored. When the extracted elementary stream is written to the pre-hard disc drive buffer 220 a, an entry is logged into the index table 237.

[0035] Although the decoder system 200 may only include a single playback data feeder 230, the decoder system 200 can play back a plurality of video elementary streams 125. During the playback of the plurality of video elementary streams 125, the host processor 205 modifies the video elementary streams 125 to allow the transport demultiplexer 205 to identify the different played back video elementary streams.

[0036] In one embodiment, the host processor 205 aligns the start of the first non-slice start code in the pictures of the video elementary streams with the start of virtual 188-byte packets. The host processor 205 then feeds single pictures from the different video elementary streams 125 in a predetermined ordering scheme. In another embodiment, the host processor 205 provides the elementary stream in the form of 188 byte packets, wherein the first byte of the packet identifies the video elementary stream.

[0037] Referring now to FIG. 4, there is illustrated a block diagram describing modifications to a video elementary stream in accordance with an embodiment of the present invention. The modifications can be used to provide single pictures from the different video elementary streams 125 in a predetermined ordering scheme. The video elementary stream 125 comprises pictures 115 representing video frames. The host processor 205 breaks the video elementary stream 125 into fixed length packets 405. For example, each fixed length packet 405 can comprise 188 bytes like transport packets.

[0038] In order for the host processor 205 to provide single pictures, the host processor 205 aligns the first non-slice start codes 410 to the start of the fixed length packets 405. Accordingly, as the host processor 205 breaks the video elementary streams 125 into fixed length packets, the host processor 205 examines the video elementary stream for the first non-slice start codes 410. When the host processor 205 finds a first non-slice start code 410, after a Slice start code, the host processor 205 breaks the packet 405 into two portions—the portion containing the data prior to the first non-slice start code 410 and the portion containing the first non-slice start code 410 and the following data. The portion containing the data prior to the first non-slice start code 410 is padded with 0's until the portion contains the fixed length of bytes.

[0039] The portion containing the first non-slice start code 410 commences a new fixed length packet 405. The fixed length packet 405 comprises the fixed length portion of the video elementary stream 125 beginning with the first non-slice start code.

[0040] The host processor 205 can provide a single picture in a series of fixed length packets 405 to the playback data feeder 235. When playing back multiple video elementary streams 125, the host processor 205 can provide packets comprising single pictures from each of the played back video elementary streams in a predetermined ordering scheme. The predetermined order scheme can comprise, for example, a round robin scheme.

[0041] Referring now to FIG. 5, there is a flow diagram for displaying a plurality of video elementary streams 125 in accordance with an embodiment of the present invention. At 505, the host processor 205 sorts the video elementary streams 125 to be played back in an order. The order can be arbitrarily selected or based on a certain criteria. At 510, the host processor 205 selects the first video elementary stream 125 in the sorted order. At 515, the host processor 205 sends a picture from the selected video elementary stream 125 to the playback data feeder 235. The picture can be sent as a set of fixed length packets representing the picture as shown in FIG. 4.

[0042] After sending the picture from the selected video elementary stream 125 at 515, the host processor 205 determines at 520, whether the selected video elementary stream 125 is the last video elementary stream 125 in the sorted order. If the selected video elementary stream 125 is not the last video elementary stream 125 in the sorted order, the next video elementary stream 125 in the sorted order is selected at 525, and 515 is repeated. If the selected video elementary stream 125 is the last video elementary stream 125 in the sorted order, 515 (selecting the first video elementary stream 125 in the sorted order) is repeated.

[0043] As host processor 205 provides each picture to the playback data feeder 230, the transport demultiplexer 225 places the pictures of the video elementary streams in the particular one of the plurality of buffers 220 c(1) . . . 220 c(n) associated with the video elementary stream.

[0044] Referring now to FIG. 6, there is illustrated a block diagram describing modifications to the video elementary stream 125 in accordance with another embodiment of the present invention. The video elementary stream 125 is broken into fixed length packets 605. The fixed length packets can comprise, for example 187 bytes. The host processor prepends each packet 605 with a header byte 605 a. The header byte 605 a stores an identifier that identifies the video elementary stream 125.

[0045] As the host processor 205 provides the modified video elementary stream 125 to the playback data feeder 230, the transport demultiplexer 225 examines the header bytes 605 a of incoming packets 605. The transport demultiplexer 225 places the packets from the video elementary streams in the particular one of the plurality of buffers 220 c(1) . . . 220 c(n) associated with the video elementary stream.

[0046] The decoder system as described herein may be implemented as a board level product, as a single chip, application specific integrated circuit (ASIC), or with varying levels of the decoder system integrated with other portions of the system as separate components. The degree of integration of the decoder system will primarily be determined by the speed and cost considerations. Because of the sophisticated nature of modern processor, it is possible to utilize a commercially available processor, which may be implemented external to an ASIC implementation. Alternatively, if the processor is available as an ASIC core or logic block, then the commercially available processor can be implemented as part of an ASIC device wherein the flow diagram of FIG. 2 is implemented in firmware.

[0047] While the invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt particular situation or material to the teachings of the invention without departing from its scope. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims. 

1. A system for playing back a plurality of video elementary streams, said system comprising: a decoder for decoding the video elementary streams; a plurality of buffers for storing the video elementary streams, wherein each of the buffers stores a particular one of the plurality of elementary streams; and a demultiplexer for distinguishing each of the plurality of video elementary streams.
 2. The system of claim 1, further comprising: a processor for writing identifiers in the plurality of video elementary streams.
 3. The system of claim 2, wherein the processor writes the identifiers in the first byte of transport packets.
 4. The system of claim 1, further comprising: a processor for providing a picture from one of the plurality of video elementary streams and providing another picture from another one of the plurality of video elementary streams responsive to providing the picture from the one of the plurality of video elementary streams.
 5. The system of claim 4, wherein the processor aligns start codes with the transport packet headers.
 6. The system of claim 1, further comprising: a start code table for associating start codes in the video elementary streams with locations in the buffers.
 7. The system of claim 1, further comprising: another memory for storing the plurality of video elementary streams.
 8. A method for playing back a plurality of video elementary streams, said method comprising: receiving the plurality of video elementary streams; demultiplexing the plurality of video elementary streams; and storing each of the plurality of video elementary streams in a particular one of a corresponding plurality of buffers.
 9. The method of claim 8, further comprising: packetizing the plurality of video elementary streams into fixed length packets.
 10. The method of claim 9, wherein the fixed length packets comprise headers storing indicators identifying particular ones of the plurality of video elementary streams.
 11. The method of claim 9, further comprising: aligning start codes with the fixed length packets.
 12. The method of claim 11, further comprising: transmitting one or more fixed length packets, wherein the one or more fixed length packets store therein, a particular picture from a particular one of the plurality of video elementary streams; and transmitting another one or more fixed length packets, wherein the another one of more fixed length packets store therein, another particular picture from another particular another one of the plurality of video elementary streams, responsive to transmitting the one or more packets.
 13. The method of claim 8, further comprising: associating start codes in the plurality of video elementary streams with locations in the buffers.
 14. An apparatus for playing back a plurality of video elementary streams, said apparatus comprising: a plurality of buffers storing the plurality of video elementary streams, wherein each of the buffers stores a particular one of the plurality of video elementary streams; and a demultiplexer connected to the plurality of buffers writing each of the plurality of video elementary streams in a particular one of the plurality of buffers; and a decoder connected to the plurality of buffers, wherein the decoder simultaneously decodes the plurality of video elementary streams stored in the buffers.
 15. The apparatus of claim 14, further comprising: a processor connected to the plurality of buffers, wherein the processor modifies the plurality of video elementary streams.
 16. The apparatus of claim 14, further comprising: a start code table connected to the processor associating start codes in the video elementary streams with locations in the buffers.
 17. The apparatus of claim 14, further comprising: a hard disc drive connected to the processor storing the plurality of video elementary streams. 